#include<cstdio>
#include<algorithm>
#include<vector>
using namespace std;

struct TreeNode{
	int val;
	TreeNode *left, *right;
	TreeNode(){}
	TreeNode(int val, TreeNode *left, TreeNode *right) : val(val), left(left), right(right) {}
};

TreeNode* dfs(vector<int> &a, int l, int r)
{
	if(l > r) return nullptr;
	if(l == r) return new TreeNode(a[r], nullptr, nullptr);
	int pos = upper_bound(a.begin() + l, a.begin() + r, a[r]) - a.begin();
	return new TreeNode(a[r], dfs(a, l, pos - 1), dfs(a, pos, r - 1));
}

void output(TreeNode *root, int fa)
{
	if(root == nullptr) return;
	output(root->left, root->val);
	printf("%d %d\n", root->val, fa);
	output(root->right, root->val);
}

int main()
{
	int n;
	vector<int> a;
	TreeNode *root = nullptr;
	scanf("%d", &n);
	a.resize(n);
	for(int i = 0; i < n; ++i)
	{
		scanf("%d", &a[i]);
	}
	root = dfs(a, 0, n - 1);
	output(root, -1);
	return 0;
}